1. Field of the Invention
The present invention relates to an axial compressor such as, for example, a fuel gas compressor or the like, and to a gas bleeding method to a thrust balance disk of such an axial compressor. The present invention particularly relates to an axial compressor which is capable of preventing damage or failure due to excessive rise in the temperature of the thrust balance disk.
2. Description of the Related Art
An example of a prior art type axial compressor will be explained in the following with reference to the fuel gas compressor shown in FIG. 5. It should be noted that this figure is a cross section showing a portion of this compressor which includes an portion of a compression section 1 at its extreme downstream position. As shown in this figure, in the compression section 1 of this fuel gas compressor, a plurality of stationary blades 3 which are fixed within casing tubes 2a on the side of a casing 2 are provided, and a plurality of moving blades 5 which are fitted coaxially around the periphery of the rotor disks 4, and these stationary blades 3 and moving blades 5 are arranged alternately along the rotational axis direction of the rotor disks 4, while being structured so as to pressurize a flow f1 of fuel gas and to expel it in the direction shown by the arrows, due to the rotation of these rotor disks 4.
At this time, a thrust force due to the reaction force which accompanies this pressurized expulsion of the fuel gas flow f1 acts upon the rotor disks 4, and the rotating body which includes these rotor disks 4 tends to be driven in the direction opposite to the flow direction of the fuel gas f1 (in the leftwards direction as seen in the figure). Since an undesirably large sized bearing would be required if it were attempted to support this large thrust force only via a bearing, accordingly, in order to avoid this, a plurality of thrust balance disks are provided coaxially with the rotor disks 4. A portion of the fuel gas flow f1 which has been compressed by the compression section 1 is taken in as a bleed gas flow f2, and thereby these thrust balance disks 6 generate a counter thrust force which opposes the said thrust force, so that it becomes possible to reduce said thrust force.
Another casing ring 2b which is fitted to the interior of the casing 2 is provided at the peripheries of these thrust balance disks, and a plurality of labyrinth seals 7 are provided against the inner circumferential surface of this casing ring 2b, so as to reduce the amount of bleed gas f2 which leaks past. Upon the upstream side of the casing ring 2b (its left side in the drawing) there is formed a partition wall 2b1 which separates the fuel gas flow f1 which is the main flow and the bleed gas f2, and a gas bleed flow conduit 8 is formed inside this partition wall 2b1 against its inner circumferential surface, while a diffuser 9 is formed against its outer circumferential surface.
The diffuser 9 is a flow conduit whose cross section area becomes greater from its upstream side to its downstream side, and thereby as the fuel gas flow f1 passes down from the compression section 1 in which speed is reduced and its pressure is recovered. The fuel gas flow f1 which exits from this diffuser 9 is discharged towards the outside of the casing 2.
On the other hand, the bleed gas f2 which flows within the bleed gas flow conduit 8 reaches the thrust balance disks 6 and presses upon these thrust balance disks 6 and the rotor disks 4 in the rightwards direction in the figure so as to exert a counter thrust force upon them. Moreover, this bleed gas flow f2 acts as a seal gas flow between the outer peripheries of the thrust balance disks 6 and the labyrinth seals 7, and then is recovered.
However, the conventional compressor described above has problems described below.
That is, although it is essential for the thrust balance disks 6 to maintain sufficient mechanical strength since they are required to receive the bleed gas flow f2 and to generate the counter thrust force, since the bleed gas flow f2 is heated up to a high temperature due to windage loss when passing down the bleed gas flow conduit 8 and due to windage loss when passing the labyrinth seals 7, therefore there is the problem that there is a danger of the thrust balance disks 6 being heated up to excessively high temperatures, so that deterioration of their mechanical strength may occur.
The present invention has been made in consideration of the above problems, and objective is to provide an axial compressor, and a method for supplying bleed gas towards a thrust balance disk thereof, which are capable of preventing reduction of the mechanical strength of the thrust balance disk due to excessive temperature increase caused by such gas bleeding.
The present invention employs the following structure to solve the above problems.
That is, according to a first aspect of the present invention, an axial compressor comprises a compression section which compresses gas to be compressed, a diffuser which reduces the speed of the compressed gas from the compression section and subjects it to pressure recovery, a thrust balance disk which receives a portion of the compressed gas as bleed gas after it has passed through the compression section and which generates a counter thrust force which opposes thrust force which the thrust balance disk experiences as reaction force due to the compression section supplying the compressed gas under pressure, and a bleed gas flow conduit which conducts a portion of the compressed gas after it has passed through the diffuser to the thrust balance disk as the bleed gas.
According to the axial compressor according to the first aspect as above, it becomes possible to cool the thrust balance disk efficiently with the bleed gas. That is, since in the prior art, the structure was such that a portion of the gas to be compressed which had a non uniform temperature distribution was supplied to the thrust balance disk directly after exiting the compression section, accordingly the bleed gas suffered an undesirable temperature rise due to windage loss before arriving at the thrust balance disk, and there was a danger of increasing the temperature of the thrust balance disk. In contrast, by the present invention, since the bleed gas which is taken from the exit of the diffuser has a uniform temperature distribution since it has been sufficiently mixed in the diffuser, and further, the bleed gas is free from any windage loss as in the prior art, accordingly it becomes possible to supply the bleed gas to the thrust balance disk at a comparatively lower temperature than in the prior art.
Moreover, the axial compressor described in a second aspect of the present invention is characterized in that the bleed gas is supplied to the thrust balance disk so as to flow in a circumferential direction which is the same as the direction in which the thrust balance disk rotates.
In a conventional compressor as described above, when the bleed gas is directly supplied at a slow relative velocity with respect to the thrust balance disk which is rotating at a high velocity, there is a danger of excessive increase of temperature of the thrust disk due to rise in the temperature of the bleed gas caused by windage loss. In contrast, with the axial compressor described in the second aspect as above, it becomes possible to keep the relative velocity difference between the bleed gas and the thrust balance disk low, since the bleed gas is supplied so as to follow the thrust balance disk in the same circumferential direction as its direction of rotation. At this time the temperature of the bleed gas which is experienced by the thrust balance disk (i.e. which impinges thereupon) is only its relatively low static temperature which is the result of subtracting its dynamic temperature from its total temperature, and accordingly it becomes possible to cool the thrust balance disk effectively. Furthermore, it becomes possible to reduce the drive power which is required for driving the compression section, due to the impact force of the bleed gas in the same circumferential direction as the direction of rotation of the thrust balance disk.
Moreover, the axial compressor described according to a third aspect of the present invention is characterized in that the bleed gas is supplied to the thrust balance disk via a TOBI nozzle (Tangential OnBoard Injection Nozzle). According to the axial compressor described in claim 3 as above, it becomes possible to supply the bleed gas to the thrust balance disk while accurately following its motion.
According to a fourth aspect of the present invention, a gas bleeding method to a thrust balance disk of an axial compressor comprises a compression section which compresses gas to be compressed, a diffuser which reduces the speed of the compressed gas from the compression section and subjects it to pressure recovery, and the thrust balance disk which receives a portion of the compressed gas as bleed gas after it has passed through the compression section and which generates a counter thrust force which opposes thrust force which the thrust balance disk experiences as reaction force due to the compression section supplying the compressed gas under pressure, wherein a portion of the compressed gas after it has passed through the diffuser, is conducted to the thrust balance disk.
According to the gas bleeding method to a thrust balance disk of an axial compressor in the fourth aspect of the present invention, just as in the case of the first aspect as above, it becomes possible to cool the thrust balance disk by the bleed gas in an efficient manner.
Moreover, the gas bleeding method to a thrust balance disk of an axial compressor according to a fifth aspect of the present invention is characterized in that the bleed gas is supplied to the thrust balance disk so as to flow in a circumferential direction which is the same as the direction in which the thrust balance disk rotates.
According to the gas bleeding method to a thrust balance disk of an axial compressor described in the fifth aspect, just as in the case of the second aspect as above, it becomes possible to cool the thrust balance disk efficiently, also it becomes possible to reduce the amount of drive power which is required for driving the compression section.
The gas bleeding method to a thrust balance disk of an axial compressor according to a sixth aspect of the present invention is characterized in that the bleed gas is supplied to the thrust balance disk via a TOBI nozzle.
According to the gas bleeding method to a thrust balance disk of an axial compressor described in the sixth aspect, just as in the case of the third aspect as above, it becomes possible to supply the bleed gas to the thrust balance disk while accurately following its motion.